The following U.S. patent publications are also noted and hereby incorporated by reference for their teachings: US 20040114631 by Aiken et al., published Jun. 17, 2004, and 20040100938 by Aiken et al., and published May 27, 2004, both of which are directed to the wireless remote control of locomotives; and 20030151520 by Kraeling et al., published Aug. 14, 2003, and teaching a rail yard remote control system for locomotives.
The railroad industry, through the Association of American Railroads (AAR) has obtained the right to use radio spectrum in the 220 MHz band for remote locomotive control. The frequency allocation consists of at least two two-way radio channels. These channels are cleared nationwide and will be used for the Remote Control Locomotive (RCL) application. Additional channel pairs in the 220 MHz band may be used at specific locations where individual licenses have been obtained.
Coexistence of RCL systems within the same block of spectrum will require a coordinated, standard method for accessing the channel(s) within the spectrum block. This is paramount to implementations in the 220 MHz band because of the very limited availability of expensive, licensed spectrum. Due to this limited number of radio channels, railroads operating in the same area may be forced to use common channels and share the repeater infrastructure. Therefore, a prime motivator for an open protocol is interoperability among user railroads and among vendors. These two dimensions of interoperability are required to maximize efficient use of limited spectrum available for this application. Vendor interoperability in this context extends down to the system level. As used herein, the term system is intended to reflect at least a single controlled locomotive (locomotive control unit; LCU) and its associated controlling devices (operating control units; OCUs). In other words, it is not anticipated that a locomotive unit would be required to operate with a controller unit from a different vendor. By ruling out this level of interoperability, the open protocol need not define message content or other details of the interactions between locomotive and controller units. This not only simplifies the specification, but also leaves room for vendor differentiation and innovation.